This invention can be utilized for optical communications, and relates to an optical switch that changes the optical propagation path by producing a mechanical displacement of the end portion of an optical fiber. It relates in particular to an optical switch for alternately switching between two optical paths comprising a pair of optical fibers.
This invention also relates to an optical switch provided at an optical fiber branch-point. It can be utilized as an optical path changeover switch in fields such as optical communications and optical instrumentation, where an optical signal propagates through optical fibers. This invention also relates to the application of micro-machining technology to optical switches.
Optical switches capable of changing the signal route by changing the path taken by an optical signal are required in telecommunication switching systems and the like. Technology is known for implementing a mechanical optical switch that causes the end portion of a movable optical fiber to oppose the end portion of either one of a pair of fixed optical fibers. With regard to this mechanical optical switch, technology is known for aligning the end portions of two opposing optical fibers by disposing the end portions of the two fibers in a single V-groove (for example, JP 8-20618 B, JP 6-273680 A, JP 6-208064 A and JP 6-265799 A).
Such optical switch technology can be used to bring the end portion of a single movable optical fiber into correspondence with the end portion of any one of two or more fixed optical fibers, and the resulting switch is termed a 1xc3x972 optical switch or a 1xc3x97n optical switch.
However, the configuration of communication circuits is such that 2xc3x972 optical switches are required. In a 2xc3x972 optical switch, the end portions of two movable optical fibers oppose the end portions of two fixed optical fibers in such manner that the optical inputs can be mutually switched between the optical outputs. This can be implemented in practice using an optical branch circuit and two 1xc3x972 optical switches, but an optical switching unit containing a large number of optical switches implemented in this way ends up being physically large and having a large optical loss due to the optical branch circuits.
A mechanical 2xc3x972 optical switch designed to overcome this problem has been disclosed in JP 8-220456 A, which describes technology for implementing an optical path switch by providing a quadrilateral hole, arranging the end portions of fixed optical fibers at two corners of this hole, arranging the end portions of movable optical fibers at the other two corners of the hole, and employing electromagnetic means to change the position of the movable optical fibers.
Although the construction disclosed in the aforementioned patent publication, namely, arranging the end portions of optical fibers at respective corners of a quadrilateral opening, is excellent, it necessitates extremely high precision machining in order to realize an optical switch with little optical loss. Namely, to align the respective optical axes of the fixed optical fibers and the opposing movable optical fibers, it is necessary to produce a mirror finish on the inner walls of the opening. An optical switch with such a construction is unsuited to mass production and would therefore be expensive. Moreover, the fabrication step of producing a mirror finish has a poor yield, and this is another reason why such a component would be expensive. Furthermore, the optical switch itself has to be of sufficient size to enable such high precision surface machining to be performed, and hence a device utilizing a large number of such optical switches is inevitably of considerable size.
The present invention has been devised in the light of this situation. It is an object of this invention to provide a small 2xc3x972 optical switch. It is a further object of this invention to provide a 2xc3x972 optical switch that is well-suited to mass production. It is yet another object of the present invention to provide an optical switch that can be manufactured inexpensively and with high yield.
According to a well-known optical fiber switch construction, the end of an optical fiber is mounted on a movable member and the position of the optical fiber end is displaced mechanically by magnetic force. It is anticipated that this construction will provide a switch capable of stable operation with little signal attenuation. Moreover, this construction is similar in idea to an electromagnetic relay and will enable a reliable, stable product with uniform performance to be mass produced.
However, there is a limit as to how small a switching element with this construction can be made. That is to say, whereas many electronic components can now be fabricated in extremely small sizes, an optical switch is still relatively large.
The present invention has been devised in the light of this situation, and it is an object of the invention to further reduce the size of an optical switch of the type that switches optical paths by producing a mechanical displacement of optical fibers.
A distinguishing feature of the present invention according to a first aspect is a construction that facilitates inexpensive high-yield mass production of a 2xc3x972 optical switch capable of mutually switching two optical communication paths comprising a pair of optical fibers.
Namely, the present invention is an optical switch comprising a pair of fixed optical fibers, a pair of movable optical fibers, a support member for supporting the end portions of these fixed optical fibers and movable optical fibers, and a drive mechanism mounted on this support member and producing a mechanical displacement of the end portions of the pair of movable optical fibers; wherein this drive mechanism includes means for producing displacement between a first position in which the optical axes of the end portions of the pair of movable optical fibers are respectively aligned with the optical axes of the end portions of the fixed optical fibers, and a second position in which the optical axes of the end portions of the pair of movable optical fibers are respectively aligned, in the reverse order to that of the first position, with the optical axes of the end portions of the fixed optical fibers. A distinguishing feature of this optical switch is that a pair of V-grooves are formed in the aforementioned support member, these V-grooves being arranged so that their opening portions are opposed and so that the end portions of the pair of fixed optical fibers are held in the respective bottom portions of the pair of grooves. A further distinguishing feature of this optical switch is that the aforementioned drive mechanism includes electromagnetic means for causing the end portions of the pair of movable optical fibers to come into contact with respective walls of this pair of V-grooves.
The support member can comprise two thin sheets stuck together, with a pair of beams formed on each such sheet. According to this construction, the pair of V-grooves appear at the face where the two thin sheets are stuck together, with the bottoms of the grooves lying within the plane at which the two sheets are stuck together. The pair of V-grooves thereby formed constitute part of an opening at the face where the two sheets are stuck together, and this opening has an hexagonal cross-section.
Preferably, the support member also includes means for holding the pair of movable optical fibers at a short distance from their ends, so that their end portions are cantilevered and their axes are positioned within a plane perpendicular to the plane containing the bottoms of the V-grooves. The aforementioned electromagnetic means preferably includes means for causing the ends of the pair of movable optical fibers to move in mutually different directions towards the walls of the V-grooves within a plane approximately perpendicular to the fiber axes, and means for causing the ends of the pair of movable optical fibers to turn through approximately 90 degrees to the left and to the right within this plane.
The aforementioned two thin sheets are silicon sheets and the grooves can be formed by etching.
The end portions of the pair of fixed optical fibers are fixed in the vicinity of one lengthwise end of the support member. The pair of movable optical fibers are fixed in the vicinity of the other end in such manner that their end faces are aligned with the end faces of the pair of fixed optical fibers and optical paths are formed. A drive mechanism is mounted on the support member, this drive mechanism producing mechanical displacement of the pair of movable optical fibers.
The end portions of the pair of fixed optical fibers are arranged horizontally with a prescribed gap (equivalent, for example, to the diameter of one of the movable optical fibers) between them, and the pair of movable optical fibers are arranged so that their end portions are perpendicular to the position in which the fixed optical fibers are mounted. This means that the movable optical fibers can be moved to two positions. In the first position, the optical axes of their end portions coincide with the optical axes of the end portions of the pair of fixed optical fibers. In the second position, the optical axes of their end portions also coincide with the optical axes of the end portions of the pair of fixed optical fibers, but the movable optical fibers have been reversed. When the drive mechanism has moved the pair of movable optical fibers one way or the other, the end portions of these movable optical fibers and the end portions of the pair of fixed optical fibers are switched to and optically coupled in either this first or second position.
A pair of V-grooves are formed in the support member that supports the end portions of the pair of fixed optical fibers, this pair of V-grooves being arranged with their opening portions opposed. The end portions of the pair of fixed optical fibers are held in the respective bottom portions of the V-grooves. Because the periphery of a fixed optical fiber is held in contact with both faces of a V-groove, the fixed optical fibers are maintained in a stable condition in which they do not slip out of the position in which they have been arranged.
An electromagnetic means is used for the drive mechanism that produces a mechanical displacement of the end portions of the movable optical fibers, and magnetic forces are employed to bring the end portions of the pair of movable optical fibers into contact with alternate walls of the pair of V-grooves. Once the end portions of the movable optical fibers have come into contact with the V-groove walls, they move along the walls and bed down into the bottom portions of opposing V-grooves. Because an electromagnetic means is used, a mechanical drive means is not needed and hence the configuration of the drive mechanism can be simplified.
The support member can be formed by sticking together two frames each formed from a thin sheet. Each frame comprises one face at which the V-grooves appear when the two frames are stuck together, a pair of beams that can be displaced to the left and the right when driven by the electromagnetic means, a linking portion which links the pair of beams to each other at their middle portion, a fixing groove for introducing and fixing the movable optical fibers, and a guide groove for guiding the movable optical fibers from the linking portion to the V-grooves. A difference in level is formed by lowering the top surface of the frame (the face at which the V-grooves appear when the two frames are stuck together) by a prescribed amount (for example, by 5 to 10 xcexcm) in the regions occupied by the pair of beams and the linking portion. This results in a space forming when the two frames are stuck together, thereby preventing the opposing beams from coming into contact with each other.
By designing the frame with a shape that has left-right symmetry with respect to a center line drawn along its longer direction, only one type of frame needs to be formed, and two of these can be stuck together to obtain the support member. This enables the number of components to be reduced.
If such frames are stuck together with the V-groove faces on the inside, a pair of opposed V-grooves are formed, and these constitute part of an opening with an hexagonal cross-section. By employing this geometry, the need for machining technology is eliminated and high-precision V-grooves can be formed without incurring high production costs.
Because a difference in level is formed between the top surface of the outer periphery of the frames and their surface in the region of the beams and their linking portion, when the two frames have been stuck together there is a space between the beams and linking portion of the top frame and the beams and linking portion of the bottom frame. This space prevents interference between the top and bottom beams and linking portion when these are displaced in different directions.
The axes of the movable optical fibers are positioned in a plane perpendicular to the plane containing the bottoms of the V-grooves (see FIG. 11 and FIG. 12), and the end faces of the movable fibers are aligned with the end faces of the pair of fixed optical fibers (see FIG. 5). The movable optical fibers are fixed in the guide grooves formed in the linking portions to give a cantilever structure.
The electromagnetic means causes the end portions of the pair of movable optical fibers to move in mutually different directions towards the walls of the V-grooves and within a plane parallel to the plane perpendicular to the plane containing the bottoms of the V-grooves. In other words, when the movable optical fiber held in the upper frame is moved to the left, the movable optical fiber held in the lower frame is moved to the right, and when the upper movable optical fiber is moved to the right, the lower movable optical fiber is moved to the left.
Accompanying the left and right movements of the movable optical fibers, their end portions make contact with the left or right V-groove faces, turn through approximately 90 degrees to the left and right along the V-shape within a plane approximately perpendicular to the fiber axes, sink into the bottoms of the V-grooves, and stop in a position in which their end faces are approximately aligned with the end faces of the fixed optical fibers. As a result, the pair of movable optical fibers and the pair of fixed optical fibers are switched to and optically coupled in a position in which their cores are approximately aligned.
Thin silicon sheets are used for the two frames that form the support member, and the V-grooves and the pair of beams and their linking portion are all formed by etching these silicon sheets.
The construction outlined above will enable a small 2xc3x972 optical switch with low optical loss to be manufactured inexpensively with high yield, and will provide a switch that is very well suited to mass production.
It will therefore be possible to mass produce, inexpensively and with high yield, a small 2xc3x972 optical switch with a construction giving low optical loss. Namely, the optical paths through the switch can be interchanged while ensuring that the ends of the two movable optical fibers always end up facing the ends of the two fixed optical fibers.
A further distinguishing feature of this invention is a construction that enables an optical switch provided at a branch point of an optical fiber to be made even smaller, and a fabrication method for this construction.
Namely, in a second aspect the present invention is an optical switch comprising a single frame, two parallel beams provided on the inside of this frame, a linking portion provided in approximately the middle of the beams and serving to interlink the beams, and a single optical fiber supported at one end of the frame and at the linking portion, and arranged parallel to the beams and so that its end portion reaches the other end of the frame. A pair of V-grooves are formed at this other end of the frame at a position contiguous with the end portion of the single optical fiber, in such manner that their opening portions are opposed and the grooves run parallel to the beams. A pair of optical fibers are arranged with their end portions in contact with the respective V-grooves. Depending on the displacement of the aforementioned single optical fiber, one or other of the ends of this pair of optical fibers faces the single optical fiber.
Preferably, the frame and the two beams are a continuous body cut from a single silicon wafer, the frame is rectangular, and the beams are formed parallel to the long sides of this rectangle.
The two parallel beams are provided on the inside of the single frame and the approximately middle portions of the beams are joined by the linking portion. A fixing groove is formed in the one end of the frame and in the linking portion, and the single optical fiber is arranged parallel to the beams and fixed in these fixing grooves. An opening is provided at the other end of the frame and parallel to the beams, and a pair of V-grooves are formed in this opening. The end portion of the single optical fiber, which has been fixed to the first end of the frame, is movably arranged between the pair of V-grooves at the end of the grooves that is nearer the linking portion, and the end portions of the pair of optical fibers are arranged and fixed in the pair of V-grooves so that, according to the displacement of the end portion of the single optical fiber, one or other of the ends of the pair of fibers will face the end of the single optical fiber.
This construction ensures that when the linking portion moves to the left or the right, the end of the single optical fiber faces the end of one or other of the pair of optical fibers in the V-grooves, thereby switching the optical path.
Magnetic members are incorporated in the linking portion, a magnet is provided on the outside of the frame, and the beams are bent and the linking portion displaced by means of magnetic force applied by the magnet. By utilizing magnetic force, the need to provide an electrical or mechanical means for displacing the beams is eliminated, whereby a smaller switch can be obtained.
With this construction the length of the longer side of the frame can be from 5 to 25 mm, thereby giving an extremely small optical switch. After the optical path has been switched, light passes directly into an opposing optical fiber, and hence this construction can provide an optical switch with only small losses occurring in the switching part.
The frame is filled with index-matching oil and packaged in a sealed container. The resistance of the index-matching oil ensures that the optical fiber moves in a stable way during switching and suppresses vibration of the end of the fiber during switching.
In a third aspect the present invention is a method for fabricating an optical switch, comprising first of all employing reactive ion etching to make an opening in the end portion of a silicon wafer where the V-grooves will be formed, then forming the V-grooves on the sides of this opening by anisotropic etching. Reactive ion etching is then employed to integrally cut out a component comprising a single frame, two parallel beams formed continuously with the frame on its inside, and a linking portion linking these beams. The bottom face of this component is joined to a base on which an indentation has been provided in the vicinity of the structure constituting the drive portion. A pair of optical fibers are inserted and fixed in the V-grooves, a single movable optical fiber is inserted and fixed in the linking portion, and the top face of this component is joined to a cover on which an indentation has been provided in the vicinity of the structure constituting the drive portion.
A distinguishing feature of the fabrication method according to this invention is that, instead of individually forming a plurality of components and then assembling these, reactive ion etching is applied to a single piece of material to form the frame and the other components in integral fashion.
Namely, the fixing grooves for the insertion of the pair of optical fibers and for the insertion of the single optical fiber arranged opposing this pair of optical fibers, are formed when the V-grooves are created. The two parallel beams provided inside the single frame and the linking portion that links the beams at approximately their middle portion, are formed integrally from one and the same piece of material. A base on which an indentation has been provided in correspondence with the position of the drive portion is then joined to the bottom face of this piece of material.
At this stage of the fabrication process, a pair of optical fibers are inserted and fixed in one fixing groove so that their end portions are in contact with respective V-grooves; a single optical fiber that will oppose this pair of fibers is inserted and fixed in the other fixing groove; and a cover provided with an indentation corresponding to the position of the drive portion is joined to the top face of the frame.
This fabrication method ensures that separate operations are no longer required for mounting the drive portionxe2x80x94within which the end portions of the optical fibers are arranged in contact with the V-groovesxe2x80x94on the beams, or for mounting the beams on the frame. As a result, further advances can be made in miniaturization, which was previously limited by the need to be able to assemble these various components. This fabrication method also decreases the number of fabrication steps involved and can therefore reduce manufacturing costs. Moreover, because fewer manual fabrication steps are involved, product quality is more stable and mass production of a highly reliable product is feasible.